Chapter III: Variation and Mutation

I have still to add a few remarks on the subject touched on in the footnote at page 31. The view there referred to was discussed by Professor Scott before in an article published in the _American Journal of Science_, Vol. XLVIII., for November, 1894, entitled "On Variations and Mutations." Following the precedent of Waagen and Neumayr, Scott sharply discriminates between the inconstant vacillating variations which it is supposed [?] produce simultaneously occurring "varieties," and "mutations," or the successively evolved _time_-variations of a phylum, which constitute the stages of phyletic development. The facts on which this view is based are those already {73} adduced in the text--the _Zielstrebigkeit_ (to use K. E. von Baer's phraseology) displayed in the visible paleontological development, the directness of advance of the modifications to a final "goal." "The direct, unswerving way in which development proceeds, however slowly, is not suggestive of many trials and failures in all directions save one." And again, "The march of transformation is the resultant of forces both internal and external which operate in a _definite manner_ upon a changeable organism and similarly affect _large numbers of individuals_."

The two points which I have here italicised are actually the facts which separate phylogenetic from common individual variation: the definite _manner_ of the change, repeated again and again without modification, and its occurrence in a _large number of individuals_.

Still the two are not solely a result of observation, deduced from paleontological data; they are also _a consequence of the theory of selection_, as was shown in the text. If the theory in its previous form was unable to fulfil this requirement, it is certainly now able to do so after germinal selection has been added, and it is not in any sense necessary to assume a difference of _character_ between phylogenetic and ontogenetic variations. Bateson and Scott are wrong in imagining that I ask them "to abrogate reason" in pronouncing the "omnipotence of natural selection." On the contrary, the theory seems to me to accord so perfectly with the facts that we might, by reversing the process, actually construct the facts from the theory. What other than the actual conditions could be expected, if it is a fact that selection favors only the useful variations and singles them out from the rest by producing them in {74} increasing distinctness and volume with every generation, and also in an increasing number of individuals? The mere displacement of the zero-point of useful variations alone must produce this effect, especially when it is supported by germinal selection. It is impossible, indeed, to see how considerable, that is perceptible, deviations could arise at all on the path of phyletic development if in each generation a large number of individuals always possessed the useful, that is, the phyletic variations? In fact, by the assumption itself, the difference between useful and less useful variations is merely one of degree, and that a slight one.

Hence, as I before remarked at page 31, I see no reason for assuming two kinds of hereditary variations, _distinct as to their origin_, such as Scott and the other palaeontologists mentioned have been led to adopt, although with the utmost caution. I believe there is only one kind of variation proceeding from the germ, and that these germinal variations play quite different roles according as they lie or do not lie on the path of adaptive transformation of the species, and consequently are or are not favored by germinal selection. To repeat what I have said in the footnote to page 31 only a relatively small portion of the numberless individual variations lie on the path of phyletic advancement and so mark out under the _guidance_ of germinal selection the way of further development; and hence it would be quite possible to distinguish continuous, _definitely directed_ variations from such as fluctuate hither and thither with no uniformity in the course of generations. The origin of the two is the same; they bear in them nothing that distinguishes the one from the other, and their success alone, that {75} is, the actual resultant phyletic modification, permits their being known as phyletic or as vacillating variations. Uncertain fluctuations along the path of evolution are what the geologists would be naturally led to expect from the theory of selection, but which they were unable to discover in the facts; it is evident, however, that these fluctuations are not a logical consequence of the theory of selection as that is perfected by germinal selection, and there seems to me to be no reason now for attributing "variations" to the union of changing hereditary tendencies, while "mutations" are ascribed to the effect "of dynamical agencies acting long in a uniform way, and the results controlled by natural selection."

The idea which the Grecian philosophers evolved of the thousands of non-adaptive formations that nature brings forth by the side of adaptive ones, and which must subsequently all perish as being unfit to live, is certainly correct in its ultimate foundations. But it is in need of far more radical refinement than it underwent in the hands of Empedocles, or than it seems likely to undergo at the hands of many contemporary inquirers. We know now that nature did not produce isolated eyes, ears, arms, legs, and trunks, and afterwards permit them to be joined together just as the play of the fundamental forces of love and hatred directed, leaving the monsters to perish and granting permanent existence only to harmonious products. Yet there is a weak echo of this conception, although infinitely far removed from its prototype, in the question as to where all the non-adaptive individuals are preserved that have perished in the struggle for existence and been eliminated from development by selection? Where, for example, are the fossil remains {76} of the rejected individuals in the line of the Horses? Certainly they should be forthcoming in far larger numbers than the individuals lying directly in the path of development, for by our very assumption the latter were greatly in the minority in every generation. Doubtless the question would be a proper one if our eyes were sufficiently keen-sighted to assign the life-value of the various minute differences that distinguish the "better" from the "worse" individuals of every generation. But this is a task which we can accomplish at best only with selective processes which are artificially directed by ourselves, as in the case of doves and chickens, and even there only with the utmost difficulty and only with reference to a single characteristic and not with any species which to-day exists in the state of nature. Picture, then, the difficulties attending such a task as applied to the meagre fossilic bones of prehistoric species, touching which the richest discoveries never so much as remotely approach to the actual number of individuals that have lived together for a _single_ generation in the same habitat. If the differences between good and bad in a single generation were striking enough to be immediately remarked _as such_ in fossil bones, the development of species would take place so rapidly that we could directly witness it in living species.

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